1. Field of the Invention
The invention relates to a method and apparatus for removing excess sodium reagent and the byproducts which are produced during the destruction and removal of polychlorinated biphenyls (PCBs) from fluids, and in particular from transformer oils. More particularly, the invention relates to a method and apparatus therefor in which the sodium is rendered less hazardous facilitating its removal from the oil for subsequent disposal, and in which virtually all of the decontaminated oil is separated from the waste products and returned for reuse.
2. Description of the Prior Art
Polychlorinated biphenyls (PCBs) are very stable compounds which are not destroyed by natural processes. Recently, their use has been banned for environmental reasons due to the possible danger to the environment and inhabitants. PCBs are not destroyed by natural processes and they are not biodegradable and will not disappear or decay to any extent by natural processes. Once they are formed, they can be destroyed only by special and expensive procedures.
Because of their thermal stability and nonflammable properties, PCBs have been used extensively as electrical insulating fluids and in dielectric materials such as in transformers and in capacitors. Although further use of PCBs for such purposes has been banned, huge quantities of these chemicals are present in the country today, especially in the electrical industry. Also, there is a vast amount of PCBs in storage awaiting a sure and inexpensive method of disposal. PCBs can be burned but only at a very high temperature and under rigidly controlled conditions. To date, incineration programs have not been entirely successful. PCBs also have been disposed of by burial, but this means of disposal presents the same risks that discourage the burial of any hazardous substance.
By the time PCBs were recognized as a hazard to health and the environment, they were widely disseminated in all compartments of the biosphere. Except in those instances where the concentration is great and the contaminated area is small, little can be done to correct the problem. Only time can do so, and the extraordinary stability of these chemicals suggests that it will be an exceedingly long time for destruction of these chemicals by natural processes. Due to the vast quantities of PCBs still in use today, eventual escape of these materials into the environment can be prevented only by an effective program and system for their destruction. It is estimated that oil-insulated transformers alone which are contaminated with more than 50 ppm of PCBs account for six hundred million gallons of contaminated oil. Add to this all the pure PCBs still in use for other purposes, and it is apparent that sensor or later a major portion of these PCBs will find their way into the environment unless a satisfactory means of disposal or destruction of PCBs is developed.
The incineration of the PCB-contaminated transformer oil used by some segments of the industry today results in the destruction of approximately twelve thousand pounds of transformer oil to get rid of approximately one pound of PCB. Likewise, the burial or incineration of PCBs or materials contaminated therewith also requires risky transportation to approved disposal sites, with the resulting dangers always present therewith.
Recently several methods have been developed for chemically removing PCBs and similar halogenated aromatic hydrocarbons from oils contaminated with such hazardous materials. One particular method and apparatus for the removal and destruction of PCBs is disclosed and claimed in my earlier U.S. Pat. No. 4,340,471. The method and apparatus disclosed in this patent has been found to be highly satisfactory for decontaminating oils containing PCBs.
However, in the continuous chemical destruction of halogenated hydrocarbons, such as PCBs, contained in the transformer insulating fluids by the apparatus disclosed in my copending application, it is necessary that an excess amount of sodium be added which is over and above the amount necessary for combining with the chlorine atoms of the PCBs to achieve maximum destruction of the PCBs. This necessitates removal of this excess sodium from the oil before it can be returned for reuse. This excess sodium is extremely difficult to remove in its elemental form by conventional techniques. Also, this elemental sodium is a hazardous material, difficult to handle and dispose. Furthermore, the polyphenyl polymer that is formed when the chlorine atoms are stripped away from the polychlorinated biphenyl molecules is an extremely difficult substance to remove from the fluid by filtration, either by itself or in combination with the excess sodium.
Unless a large portion of these substances is removed from the oil by some means other than filtration, the excess sodium and byproducts will clog the filters including Fuller's earth beds, requiring frequent changing of the filter medium. Since the frequent changing of filter medium is troublesome and costly, and since the discarded filter medium carries with it a certain amount of valuable oil, it is desirable that the filter medium be used as long as possible before eventually being replaced.
There is no known method and apparatus of which I am aware which enables the excess sodium reagent and byproducts of reaction which are produced during the destruction and removal of halogenated aromatic hydrocarbons from fluids, and particularly PCBs from oil, to be removed from the oil in a relatively inexpensive and highly efficient manner other than my method and apparatus set forth and described below.